1. Field of the Invention
The present invention relates generally to print systems, printer drivers and printers, and more particularly to a print system, a printer driver and a printer for use in driving a print head for carrying out serial printing.
2. Description of the Related Art
In a typical conventional print system; for example, in a serial non-impact ink-jet printer, it has been arranged that one-way or two-way printing is set selectable when monochromatic text data as to characters, numerals, ruled lines and the like is printed. By the one-way printing is meant that printing is carried out in one fixed direction and called a high-quality image printing mode, whereas the two-way printing means that printing is carried out in both lateral directions and called a high-speed printing mode.
In the case of one-way printing, printing is carried out in one fixed direction at all times and consequently printing time tends to increase as a printing pass, that is, the movement of a print head increases. However, one-way printing is advantageous in that high-quality printing can be carried out because the influence of a shift in the printing position due to the mechanical precision and the like of the print head is minimized.
In the case of two-way printing, on the other hand, printing can be carried out in both lateral directions and consequently the printing pass is halved in comparison with one-way printing, so that printing time is shortened. Since a shift in the printing position affects two-way printing, however, printing quality lowers as the discontinuity of printing dots becomes visually conspicuous when printing dots vertically linked together (in the sub-scanning direction) like vertically-double-sized characters and vertical ruled lines are printed.
For the reasons stated above, the user is allowed to designate either one-way or two-way printing to be used each time one printing job is done, that is, on a document basis by taking into consideration the character of a document to be printed. The user who prefers high-speed printing designates two-way printing, whereas the user who desires high-quality printing designates one-way printing. The whole printing job is controlled by the designated printing mode. When, therefore, one-way printing is designated, the one-way printing is totally employed for printing a document even though there exits a portion containing full-sized characters therein, whereas when two-way printing is designated, the two-way printing is totally employed even though there partially exist vertically-double-sized characters, vertical ruled lines and the like therein.
However, a document to be printed usually has, in combination, a portion containing full-sized characters and the like whose printing quality is free from deterioration ever when they are subjected to two-way printing, and another portion containing vertically-double-sized characters and the like whose printing quality is lowered unless they are subjected to one-way printing. Therefore, the designation of the one-way printing or two-way printing on a printing job basis results in increasing printing time due to an increase in undesired printing pass or otherwise nonconformity resulting from a partial deterioration in printing quality.
Japanese Patent Publication No. Hei. 4-9153 (Kokoku), Japanese Patents Publications No. Hei. 2-233275 and No. Hei. 8-11353 (Kokai), for example, disclose the art of deciding which one of the one-way and two-way printing to choose by analyzing the image data that have been developed.
In the art described in Japanese Patent Publication No. Hei. 4-9153 (called the art described in the first publication), one-way printing is employed when the number of vertical dots is greater than predetermined width in a pattern that is developed and when a character pattern is imaged into a plurality of zones, whereas two-way printing is employed when a character pattern is imaged in a single zone.
In the art described in Japanese Patent Publication No. Hei. 2-233275 (the art described in the second publication), a decision is made on whether two-way printing or one-way printing is used according to the position where a vertical dot-line break is detected.
In the art described in Japanese Patent Publication No. Hei. 8-11353 (called the art described in the third publication), a decision is made on the reversion or non-reversion of the direction in which a print head is fed by analyzing the dimension in the height direction of a character string on the basis of attribute information and taking into consideration the continuity of image data.
In the art described in the first publication, one-way printing can be switched to two-way printing and vice versa, depending on the size of the developed character pattern. Therefore, it is possible to make not only printing time shorter but also printing quality better than in the art of choosing between one-way and two-way printing on a printing job basis.
However, in the art described in the first publication, the selection of one-way printing or two-way printing is only based on whether the character pattern on a certain line has been zoned and no consideration has been given to the relation in size between the character pattern and other character patterns located above and below the character pattern in question. Consequently, an undesired printing pass cannot completely be removed and the problem is that the shortest printing time has not been attained yet. When a character pattern on a certain line consists of full-sized characters, for example, this line is printable through one main scanning. Nevertheless, there is a case where the printing pass is not reducible unless the relation with other adjoining lines is taken into consideration.
Similarly in the art described in the second publication, the number of printing passes may increase, depending on the relation between the height of the character string that follows the dot-line break and the head dimensions, since no consideration has been given to the size of the next image data that follows the dot-line break thus detected.
The art described in the third publication is superior in point of the fact that the apex and the lowest part of a character are detected according to the attribute information, and even the presence or absence of the apex of a character on the next line, that is, the next character data that follows the blank area and image data are taken into consideration. In the art described in the third publication, however, the printing of the whole data stored in a buffer is controlled by the printing direction obtained by analyzing the attribute information. More specifically, the specific printing logic based on the analysis of attribute information is applied to the whole data stored in the buffer and intended for printing. Notwithstanding, the art described in the third publication is still problematical in that each time a blank area having no data to be printed is actually detected, there may arise a case where it is needed to decide whether to reverse the printing direction in the blank area or to print printing areas before and after the blank area; in other words, the art described therein is incapable of dealing with this case.